(1) Field of the Invention
This invention relates to the method of fabrication of alignment posts and optical interference layers directly on silicon wafers with liquid crystal material and to the unique resulting device structure.
(2) Description of the Prior Art
The picture quality of liquid crystal displays from a simple seven segments to millions of pixels is determined by the structure used to control the variation of thickness and position leads after wafer processing. There are known processes for creating insulated alignment posts based on preformed glass microspheres and rods; relatively low series resistance posts can be obtained by means of selective deposition of polysilicon and metallic silicide. (Making of metallic vias and contacts are a comparatively well known processing art.)
U.S. Pat. No. 5,498,925 to Bell et al describes the formation of posts in flat panel displays using processes based on a heat-treated slurry or paste upon a glass plate. U.S. Pat. No. 5,597,736 teaches the function of a light-blocking layer deposited upon a semiconductor substrate material that can emit light. Until now, it has been difficult to construct alignment posts using photolithography and also add optical interference layers simultaneously onto a semiconductor substrate material.
A principal object of the present invention is to describe a new structure for building a flat-panel liquid-crystal display upon an integrated circuit (IC) die with inter-related alignment between the posts supporting the overlaying glass cover plate and optical interference layers (OIL) employed to improve image quality. The alignment posts are made of silicon nitride, and the OIL of silicon nitride/oxide multilayers.
Another object of this invention is to describe effective and very manufacturable methods of photolithographic formation of insulating alignment posts (also called studs or pillars). These methods can be used in processing many different device types, and are described in this application for liquid crystal display devices as a way of illustrating their embodiment at a pixel density beyond that achievable with preformed micro-glass spheres and rods.
A further object of the present invention is to describe methods of deposition for both the posts and the optical interference layers that are independent of each other and retain their desired feature during deposition of subsequent features.
In accordance with the objects of this invention, a new method of forming insulating material alignment posts associated with active device structures is achieved. A silicon wafer having patterned active device therein and thereon is formed and the insulating posts are deposited in a pattern over active device structures. Furthermore a device structure that combines insulating materials for alignment posts and optical interference layers associated with an active device structure in a silicon body is achieved. A silicon semiconductor wafer having patterned active silicon device structures and alignment posts is formed and the whole structure is covered with an optical interference layer.